Embodiments disclosed herein are related to the art of color image rendering. For the most part, they will be described with reference to color image printing. However, methods and systems disclosed herein are applicable to other rendering technologies, such as, for example, color image displays.
In general, image rendering processes are physical in nature. That is, image rendering processes rely on physical structures which can influence rendered image quality and consistency. For instance, variation in phosphor quality or density in a cathode ray tube (CRT) or plasma display, light emitting diode (LED) efficiency in an LED display, and/or spatial variation in the light output of a fluorescent back light in a liquid crystal display (LCD) can cause color appearance variations across the surface of a display device. In printing systems, physical alignments, component tolerances, wear and component age can influence the uniformity with which colorants such as inks and toners are laid down across the surface of print media.
Techniques for spatial uniformity compensation have been developed. For instance, the concept of compensating tone reproduction curves (TRCs), which have been used to calibrate or compensate the overall application of individual colorants in a particular rendering device or print engine, has been extended to include spatial specificity.
For instance, test patches or strips are printed based on individual colorant target gray levels or lightness. Measurements are made of actual or rendered colorant lightnesses or gray levels at various positions across the surface of the test patches or strips. Spatially dependent compensating functions are generated based on these measurements. In operation, desired or target colorant contone, gray level or lightness levels and associated position information are processed through these colorant-specific, spatially dependent compensating functions to generate or determine a compensated colorant contone, gray level or lightness value for the desired position. As such, colorant-specific, spatially dependent compensating functions can be used to improve image quality in a rendering device or printer.
In order to increase throughput, some printers and copiers are being developed which include two or more marking engines. For example, U.S. patent application Ser. No. 10/924,113 filed Aug. 23, 2004 by Jonas M. M. deJong, et al. for a Printing System with Inverter Disposed for Media Velocity Buffering and Registration; U.S. patent application Ser. No. 10/924,106 filed Aug. 23, 2004 by Robert M. Lofthus, et al. for a Printing System with Horizontal Highway and Single Pass Duplex; U.S. patent application Ser. No. 10/924,459 filed Aug. 23, 2004 by Barry P. Mandel, et al. for a Parallel Printing Architecture Consisting of Containerized Image Marking Engine Modules; U.S. patent application Ser. No. 10/860,195 filed Jun. 6, 2004 by Robert M. Lofthus, et al. for a Universal Flexible Plural Printer to Plural Finisher Sheet Integration System; U.S. patent application Ser. No. 10/881,619 filed Jun. 30, 2004 by Daniel G. Bobrow for a Flexible Paper Path Using Multidirectional Path Modules; U.S. patent application Ser. No. 10/761,522 filed Jan. 21, 2004 by Barry P. Mandel, et al. for a High Print Rate Merging and Finishing System for Parallel Printing; U.S. patent application Ser. No. 10/785,211 filed Feb. 24, 2004 by Robert M. Lofthus, et al. for a Universal Flexible Plural Printer to Plural Finisher Sheet Integration System; and U.S. patent application Ser. No. 10/917,768 filed Aug. 13, 2004 by Robert M. Lofthus for a Parallel Printing Architecture Consisting of Containerized Image Marking Engines and Media Feeder Modules, all of which are incorporated herein by reference, describe aspects of tightly integrated document processing systems including a plurality of marking engines.
Additionally, some printers and copiers are being developed using a hypermodular structure to increase modularity and flexibility. These systems may possess a number of distributed processors, sensors, and actuators. For example, U.S. patent application Ser. No. 10/357,687 filed Feb. 4, 2003 by David K. Biegelsen, et al., for Media Path Modules; U.S. patent application Ser. No. 10/357,761 filed Feb. 4, 2003 by Markus P. J. Fromherz, et al., for Frameless Media Path Modules; U.S. patent application Ser. No. 10/740,705 filed Dec. 19, 2003 by David K. Biegelsen, et al., for a Flexible Director Paper Path Module; and U.S. patent application Ser. No. 10/812,376 filed Mar. 29, 2004 by David G. Duff, et al., for a Rotational Jam Clearance Apparatus, all of which are incorporated herein by reference, describe aspects of tightly integrated document processing systems including hypermodules.
The concept of colorant-specific, spatially dependent compensating functions has been further extended to address consistency across a space of desired uniformity that extends across a plurality of marking engines and across time. For example, U.S. patent application Ser. No. 10/922,316, cross referenced above, and U.S. patent application Ser. No. 10/923,166 by Zhang, et al., entitled UNIFORMITY COMPENSATION IN HALFTONED IMAGES filed Aug. 20, 2004, the disclosure of which is totally incorporated herein by reference, discuss the application of sets of colorant-specific, spatially dependent compensating tone reproduction curves (TRCs) over temporal and spatial spaces of desired uniformity that extend across multiple rendering devices or print engines.
Colorant-specific, spatially dependent compensating functions can provide substantial improvements in image quality and image consistency. However, they do not compensate for colorant appearance effects that are correlated to colorant interactions.
In offset printing, the efficiency with which an ink is absorbed or trapped can be influenced by the presence of another ink laid down earlier. Additionally, trapping efficiency is a function of transfer roller pressures. Spatial variations in those pressures may cause spatial variation in interacting colorant appearance. Related colorant appearance variations associated with print-head-to-print-media spacing variations associated with ink jet technology are also anticipated. In electrophotographic processes, spatial variations, due to, for example, manufacturing tolerances, wear, dirt and component age may produce spatially dependent charge, development field, cleaning field, toner concentration, raster output, raster output power, and/or roller pressure variations which may manifest as spatially dependent colorant appearance nonuniformities or variations. Some component or portion of these colorant appearance variations or nonuniformities may be correlated to interactions between colorants.
Therefore, there has been a desire for methods and systems for compensating for correlated or colorant interaction related colorant appearance variation effects.